This study seeks to gain understanding of the human postural system and its ability to adapt to external visual perturbations. The adaptation, habituation and saturation characteristics of postural sway in healthy individuals standing on different support surfaces will be studied as will as the same characteristics in patients with diseases that impair balance such as vestibular deficits and cerebellar deficits. The focus will be on the time-varying aspects of the postural response to visual perturbations. Preliminary data indicate that the ability to adapt to perturbations can be used to distinguish between classes of subjects. The primary tool for data collection is a center of pressure (COP) platform type with a moving visual field device attached. Data processing methods such as time-frequency analysis are employed to allow the calculation of adaptation (per-stimulus response decline within a trial), habituation (a decrease in response to stimuli across repeated trials) and saturation (compression of the response to increasing stimulus) statistics with high confidence. An objective of the research is to improve the evaluation and rehabilitation of individuals with balance disorders.